1. Field of the Invention
The present invention relates to an isocyanatoalkyl (meth)acrylate substantially free of hydrolyzable chloride, which is obtained by removing hydrolyzable chloride from an isocyanatoalkyl (meth)acrylate containing hydrolyzable chloride, and a production method therefor. The isocyanatoalkyl (meth)acrylate substantially free of hydrolyzable chloride provided by the present invention is useful particularly as a material or raw material of a photoresist and the like for electronic materials.
In the present invention, unless otherwise indicated, the term "(meth)acrylate" includes acrylate and methacrylate.
2. Description of Related Art
The isocyanatoalkyl (meth)acrylate represented by 2-isocyanatoethyl methacrylate is a compound containing both an isocyanato group highly reactive with a compound having an active hydrogen, for example, a compound having a substituent such as a hydroxyl group or a primary or secondary amino group and a vinyl polymerizable carbon-carbon double bond within the same molecule. This is an industrially very useful compound and it is used in many applications such as paints, coating materials, adhesives, photoresists, dental materials and magnetic recording materials. This compound is produced using phosgene as described in U.S. Pat. No. 2,821,544 and JP-A-54-5921 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and in general, contains an impurity called "hydrolyzable chloride". (In the present invention, unless otherwise indicated, the term "hydrolyzable chloride" means chlorine in a chlorine-containing compound which is hydrolyzable.) A representative example of the compound is a chlorine-containing compound such as (meth)acryloyloxyalkylcarbamoyl chloride present in a product containing the desired object in the production of an isocyanatoalkyl (meth)acrylate.
If a urethane acrylate or the like is produced using an isocyanatoalkyl (meth)acrylate containing a hydrolyzable chloride, the hydrolyzable chloride acts as a catalyst poison. Moreover, the chlorine compound mixed with a product adversely affects weatherability and corrosion resistance. In particular, the presence of hydrolyzable chloride may be fatal to the photoresist material for electronic equipment use.
Heretofore, various methods for reducing the hydrolyzable chloride in an isocyanato compound in general have been disclosed.
For example, JP-A-53-119823 discloses a method of mixing a hydrolyzable chloride-containing isocyanato compound with a fine alkali metal carbonate at a high temperature for a long period of time. JP-A-59-172450 discloses a method of adding a carboxylate of zinc and a hindered phenol-type antioxidant to a hydrolyzable chloride-containing isocyanato compound and subjecting the mixture to heat treatment and then distillation. U.S. Pat. No. 3,465,023 discloses a method of synthesizing an isocyanate in a water-insoluble solvent and then rinsing it with an aqueous sodium hydrogen carbonate solution; and German Patent 2,249,375 discloses a method of treating a hydrolyzable chloride-containing polymethylenepolyphenyl isocyanate with an epoxy compound.
Furthermore, as a method which does not use chemicals such as an alkali metal carbonate described above, JP-A-61-161250 discloses a method of vaporizing a hydrolyzable chloride-containing isocyanato compound and then purifying the isocyanato compound by condensation at a temperature of 70.degree. C. or higher.
However, these methods cannot achieve satisfactory reduction of hydrolyzable chloride or have various problems to be solved in their industrial implementation. For example, according to the method of mixing a hydrolyzable chloride-containing isocyanato compound with an alkali metal carbonate at a high temperature described in JP-A-53-119823, the isocyanato compound and the carbonate after treatment are difficult to separate, which gives rise to inevitable generation of loss. The method involving rinsing with an aqueous sodium hydrogen carbonate solution described in U.S. Pat. No. 3,465,023 is disadvantageous in that white insoluble matters precipitate at the boundary between an organic phase and an aqueous phase and this renders the subsequent separation operation cumbersome or causes staining of the apparatus. Furthermore, these methods have the concern that isocyanato compound is contaminated with sodium ion. Even if the sodium ion content is on the order of ppm, a serious problem arises in using the isocyanato compound in electronic materials.
Particularly, in purifying an isocyanato compound having a carbon-carbon double bond, the hydrolyzable chloride content must be effectively reduced while preventing a polymerization reaction between the isocyanato compounds with each other, However, satisfactory results cannot be achieved by the above-described methods.
U.S. Pat. No. 4,310,688 discloses a method of treating a methylene chloride solution of isocyanatoethyl methacrylate containing 0.21% of hydrolyzable chloride with a vicinal epoxy group-containing compound (e.g., 1,2-butylene oxide) to thereby reduce the hydrolyzable chloride content to 0.05%. However, by this method, the hydrolyzable chloride content can be reduced at most only to hundreds of ppm and the purified isocyanato compound obtained does not have sufficient properties for use in electronic materials.
In order to solve these problems in conventional techniques, the present inventors have proposed a method of reducing the hydrolyzable chloride content in an isocyanato compound by treating it with an epoxy compound in the presence of an amine (JP-A-9-323958). This method is an excellent method but still fails to achieve complete removal of hydrolyzable chloride.
On the other hand, a method of producing an isocyanato compound without using phosgene has also been studied. For isocyanatoalkyl (meth)acrylate, a method using thermal decomposition of a urethane compound has been proposed (see, U.S. Pat. No. 2,718,516, JP-A-62-10053, JP-A-62195354, JP-A-5-186414, JP-A-5-186415 and JP-A-6-263712). This method comprises a step of thermal decomposition at a high temperature and since the isocyanatoalkyl (meth)acrylate is very readily polymerized, the yield is not satisfactory by any means in view of profitability.